The interrelationship between the compaction behaviour and the mechanical strength of pure pharmaceutical tablets

This paper presents and analyses data obtained from the uniaxial compaction of pure pharmaceutical powders in terms of a number of mechanical properties, and correlates these data to some aspects of fracture mechanics. This includes seven different types of pharmaceutical drugs and excipients: alpha lactose, microcrystalline cellulose (Avicel PH 102), acetylsalicylic acid (Aspirin), dicalcium phosphate, magnesium carbonate, acetaminophen (Paracetamol) and starch. The powders were compacted to various ultimate normal stresses ranging between 25 and 246 MPa in an instrumented (force/displacement) single-ended axial compression in cylindrical die with planar punches. The results clearly demonstrate that, to some extent, the toughness of a tablet may be interpreted directly from some mechanical characteristics of its compliance response, i.e., the plastic work and the plasticity index, during the compaction process.     

关于金刚石微粉强度问题探讨

拉曼光谱通过测定金刚石微粉颗粒的晶体结构及内部缺陷和杂质含量评价微粉强度品级,是一种科学、有效、能快速检测金刚石微粉强度品级的方法.根据拉曼光谱测定金刚石微粉强度品级,研究了金刚石微粉强度与金刚石单晶原料强度、金刚石原材料的合成时间、微粉生产工艺和微粉表面处理工艺之间的关系.结果表明,金刚石微粉的强度虽然与原材料强度品...     

Low-temperature sintering of coarse alumina powder compact with sufficient mechanical strength

Coarse alumina powder compacts doped with various amounts of titania and copper oxide were pressurelessly sintered from 900 °C to 1600 °C. Their phase assemblages and microstructural evolution, as well as their properties, were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry/thermogravimetric (DSC/TG) analysis, and three-point bending and wetting test. The role of TiO₂ and CuO during the sintering is discussed in detail. The experimental results show that the liquid phase from the copper oxide appeared at approximately 1200 °C, so the solid-state reaction between alumina and titania took place at a lower temperature. Such solid state-reaction sintering had a strong impact on the grain growth and greatly promoted the densification of the alumina compact. In addition, the liquid phase inhibited the abnormal grain growth and microcracking. As a result, the coarse alumina powder compacts doped with 5 wt% TiO₂–CuO were fully densified and exhibited sufficient flexural strength (342±21 MPa) when sintered at a temperature of 1450 °C for 2 h.     

Influence of compaction on the interfacial transition zone and the permeability of concrete

The interfacial transition zone (ITZ) is regarded as a key feature for the transport properties and the durability of concrete. In this study one self-compacting concrete (SCC) mixture and two conventionally vibrated concrete (CVC) mixtures are studied in order to determine the influence of compaction on the porosity of the ITZ. Additionally oxygen permeability and water conductivity were measured in vertical and horizontal direction. The quantitative analysis of images made with an optical microscope and an environmental scanning electron microscope shows a significantly increased porosity and width of the ITZ in CVC compared to SCC. At the same time oxygen permeability and water conductivity of CVC are increased in comparison to SCC. Moreover, considerable differences in the porosity of the lower, lateral and upper ITZ are observed in both types of concrete. The anisotropic distribution of pores in the ITZ does not necessarily cause anisotropy in oxygen permeability and water conductivity though.     

Mechanical energies associated with compaction of form I and form II paracetamol powder

Paracetamol solid state has three known polymorphic forms; monoclinic form (Form I), orthorhombic form (Form II) and Form III. In this work Form II was successfully produced in appreciable quantities by controlled crystallization of melted Form I. The moisture content of both forms stored for 3 weeks at 25 °C at different relative humidity conditions was investigated. It was found that neither form acquires any significant amount of moisture in any of the storage conditions. The results showed that Form II is stable for 3 weeks of storage at relative humidities of 23%, 43%, and 58%. Work of compression, work of decompression, plasticity index (ψ), and elastic energy/plastic energy (EE/PE) ratio associated with the compaction of both forms were determined at maximum applied compression forces of 35 kN, 27 kN, 18 kN, 11 kN, and 5 kN. It was found that both forms have high magnitude of elastic energy recovery during decompression. Moreover, it was found that for generating compacts of equal volumes of the two forms the plasticity index is larger for Form II and the EE/PE ratio is larger for Form I.     

The implications of the determination of the mechanical strength of powder compacts containing a pre-formed hole

Powder compacts of two pharmaceutical model materials, microcrystalline cellulose (MCC) and α-lactose monohydrate (LM), have been prepared, at approximately the same porosity, in the form of discs with and without a central hole. The ratio of the inner to outer diameters for the ring compacts was 0.088. To achieve the equivalent porosities, higher pressures were required for the discs in which a central hole was formed. The compacts were subjected to diametral compression, and the force to cause failure was recorded. The values of the tensile stress to cause failure in the discs with holes were derived from the approach of Durelli and Lin [J. Appl. Mech. 53 (1986) 213]. For MCC, the values of tensile strength for compacts without a hole were higher than for those with a hole, but the opposite was true for LM. The approach also allowed the calculation of values for the compressive and tensile stress at the inner and outer boundaries of the ring. Values for both the ratio of the inner tensile stress and the inner compressive stress to that of the tensile strength of a compact without a hole clearly differed from those suggested by Hiestand et al. The value for the stress concentration factor is an essential feature of the calculation of a factor used by these authors in the prediction of the compaction properties of powders, the “brittle fracture propensity” (BFP). These differences, coupled with the incorrect method of calculating the value of the tensile stress of a compact with a central hole from the breaking force, indicate that the derivation of the BFP has no theoretical basis.     

Study on the mechanical strength of primary carbonate tablets

The mechanical strength of three carbonate tablets constructed by uniaxial compaction is evaluated using a simple tester, specially designed, as a comparative method, to classify and establish correlations between the measured resistance and the physical and flow properties of each carbonate. The net compression work required to construct the tablets is also compared with the strength of the samples in order to relate it to powder's ability to convert the force applied into effective solid-solid bonds.     

High-velocity compaction of titanium powder and process characterization

Pure titanium powder was pressed into two kinds of samples through high-velocity compaction technology. The first was rings with 60 mm outer and 30 mm inner diameters and a mass of 57 g, and the second was cylinders with 20 mm diameter and a mass of 10 g. For the rings, the maximum shapable relative density reached 76.2% at impact energy of 2283 J. For the cylinders, however, it reached 96.0% at much lower impact energy of 1217 J. The reasons for the contradictory effects were analyzed, and a new quantity, impact energy per unit mass, was put forth to well characterize the difference. In addition, the relations between peak pressure and green density of the two kinds of samples were found to comply with Huang Pei-yun equation, and the densification mechanism was discussed.     

Influence of chemical degradation on mechanical behavior of a petroleum cement paste

Cement paste used in the Oil Industry is generally subjected to chemical degradation due to flow of acid fluids in various situations. The present study focuses on the evolution of thermo-hydro-mechanical (THM) behavior with chemical degradation of petroleum cement paste. Triaxial compression tests with different confining pressures (0, 3, 10 and 20 MPa) are carried out on a standard oil cement paste in sound state and completely degraded state by ammonium nitrate solution under a temperature of 90 °C. The results obtained show that the material in its initial state exhibits a small elastic phase and a strong capacity of compaction. The mechanical behavior depends on the load induced pore water pressure. Because of the increase in porosity caused by chemical degradation, the mechanical strength (cohesion and friction angle) and Young's modulus decrease. The dependence of mechanical strength and Young's modulus on confining pressure is smaller in the chemically degraded cement paste than in the sound one. In fine, the mechanical behavior of the whole material becomes more ductile. As a result, such effects of chemical degradation should be taken into account when modeling such cement paste materials exposed to such chemical degradations.     

The effect of spraying temperature on the corrosion and wear behavior of HVOF thermal sprayed WC-Co coatings

Cobalt matrix carbides are favorite cases of wear and corrosion-resistant coatings. Among thermal spray processes the high-velocity oxy-fuel (HVOF) spraying is a popular choice because of its unique properties. In this paper the effect of particles’ temperature on the porosity, corrosion as well as wear behavior of high-velocity oxy-fuel (HVOF) thermally sprayed WC-12Co coating has been studied. The temperature of particles was measured using a Spray-Watch diagnostic system. Also the scanning electron microscopy (SEM), image analysis, and X-ray diffraction (XRD) were used for examining the powder and the coating. The corrosion potential and corrosion current density was evaluated using potentio-dynamic polarization test. Results show that the porosity is affected by thermal flow on the coating surface. Besides, a higher particle temperature resulted in achieving more amorphous phases and eventually the higher corrosion resistance. Sample A was coated with an impact temperature of 2012.4 °C. Although the porosity was higher than other sprayed samples (1.7%), the higher content of amorphous phase led to recording a higher corrosion resistance (64.3E-6A). Sample B was coated with an impact temperature of 1880 °C for which the Jcorr was 67.2E-6 A. Sample C was sprayed with a low impact temperature of 1702 °C for which a surface porosity of 1% and the low corrosion resistance of 79.5E-6A were recorded. Based on the experiments it was concluded that for the WC-12Co coating the corrosion resistant phases have the dominant influences on the corrosion resistance.     

Effect of slurry properties and operational conditions on the structure and properties of porcelain tile granules dried in an acoustic levitator

Spray-drying is a unit operation highly important in many industrial applications. In this work, the influence of the drying conditions on the final grain properties has been investigated in single droplet experiments. Porcelain tile suspensions like those used in industry have been used. The experiments have been carried out in an acoustic levitator modified to work at high temperature conditions. The effect of the flocculation state, initial solid mass load, primary particle size, air temperature and initial droplet volume on the mean porosity of the grain and its mechanical strength has been studied. The most important parameters to be considered for the porosity are the primary particle size, the initial solid mass load and the flocculation state. For the mechanical strength the significant effects are the primary particle size, the initial solid mass load, the air temperature and the cross effect of flocculation state and initial solid mass load.     

Effect of Nb2O5 content and sintering temperature on the microstructure and bending strength of porous Ni-YSZ cermets

Porous Ni-YSZ cermets are prepared by reducing NiO-YSZ composites upon exposure to (Ar+6% H₂) gas. The porous cermets are prepared by the addition of carbon black (0.123 mol) to mixed NiO-YSZ powders and the conversion of NiO to Ni in the NiO-YSZ composites. The microstructure and bending strength of porous Ni-YSZ cermets as functions of sintering temperature and Nb₂O₅ content are discussed. The Ni-YSZ cermets consist of uniformly distributed Ni and YSZ grains as well as pores. Both higher sintering temperature and higher Nb₂O₅ content yield lower porosity, thus increasing the bending strength. The bending strength of 0.00470 mol% Nb₂O₅–containing Ni-YSZ cermets sintered at 1400 °C (111 MPa) is about two times higher than that of Nb₂O₅–free Ni-YSZ cermets sintered at 1400 °C (59 MPa).     

Influence of modified multi-walled carbon nanotubes on the mechanical behavior and toughening mechanism of an environmentally friendly granulated blast furnace slag-based geopolymer matrix

This study aimed to investigate the mechanical behavior of an environmentally friendly granulated blast furnace slag-based geopolymer matrix reinforced with modified multi-walled carbon nanotubes (MWCNTs). The modified MWCNTs were obtained using a modification method combining nitric acid and sulfuric acid and were then dispersed using sodium dodecylsulfate (SDS) as a dispersant. Two types and three concentrations of MWCNTs were mixed directly into the aqueous solution, sonicated, and then mechanically mixed with waste granulated blast furnace slag to form the geopolymer matrix. Raman and Fourier transform infrared (FT-IR) spectroscopy were used to evaluate the ordered structure and crystallization degree of the modified MWCNTs. Then, the dispersity of the modified MWCNTs was characterized using transmission electron microscopy (TEM). The compressive and bending strengths were measured to evaluate the mechanical behavior of specimens. Moreover, the polycondensation products, polycondensation degree, pore structure, and microscopic morphology of the geopolymer matrix were analyzed using X-ray diffraction (XRD), FT-IR spectroscopy, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS). The experimental results showed that the incorporation of 0.1% functionalized MWCNTs had an optimal influence on the fluidity and mechanical behavior. The slump diameters of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 23.5%, respectively, compared with the reference geopolymer matrix. For geopolymer matrix samples at a curing age of 28 d, the compressive strength of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 17.6%, respectively. For the bending strength, the corresponding increases were 17.6% and 18.7%, respectively. It was found that functionalized MWCNTs could increase the degree of polycondensation, leading to a more traditional amorphous N-A-S-H phase, a finer C–S–H phase, more Q⁴ (2Al) and Q⁴ (3Al), and lower porosity. In addition, the propagation of micro-cracks in the geopolymers was inhibited by the incorporation of functionalized MWCNTs.     

Synthesis of nanocrystalline 8 mol% yttria stabilized zirconia powder from sucrose derived organic precursors

An organic precursor synthesis of 8 mol% yttria stabilized zirconia (YSZ) powder from Zr–Y composite nitrate solution and sucrose has been studied. Oxidation of sucrose in Zr–Y composite nitrate solution containing excess nitric acid in situ generates hydroxy carboxylic acids that forms a white sol which showed peaks at 1640 cm⁻¹ and 1363 cm⁻¹ in IR spectrum corresponding to hydroxy carboxylic acid complexes of Zr and Y. Precursor mass obtained by drying the sol on calcinations at 600 °C produced loosely agglomerated particles of cubic YSZ. Deagglomerated YSZ contain submicron particles with D₅₀ value of 0.5 μm and the particles are aggregates of nanocrystallites of nearly 10 nm size. Compacts prepared by pressing the YSZ powder sintered to 96.7% TD at 1450 °C. The sintered YSZ ceramic showed an average grain size of 2.2 μm.     

Synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics

To explore the synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics, blast furnace slag was chosen as the main material, and glass fibre and Al powder as reinforcement materials. The phase compositions, microstructures, compressive properties, and apparent density of the glass-ceramics with varying quantities of glass fibre and Al powder were investigated. The experimental results indicated that Al powder could exist as a simple substance in glass-ceramics and form a dense net coating on the surface of blast furnace slag to improve the plasticity of the glass-ceramic. The glass fibre had better reinforcement effect than Al powder because of its extremely high mechanical strength. The plasticity of glass-ceramics, however, severely decreased; the glass-ceramics exhibited brittle failure during compression. A slight increase in the content of CaSi₂ and SiO₂ in the glass-ceramics was closely related to the addition of glass fibre. Considering safety and economy, glass-ceramics with 6% Al and 14% glass fibre (S4) have the best mechanical properties. The compressive strength, strain at maximum force, and apparent density were 40?MPa, 19% and 1.974?g/cm³, respectively.     

Influence of silane‐modified coconut shell powder on thermal and mechanical properties of thermoplastic elastomers

A silane coupling agent (glycidyloxypropyltrimethoxysilane, GPTMS) was used to modify coconut shell powder (CSP), and the influence of the modified coconut shell powder (G‐CSP) on the thermal and mechanical properties of thermoplastic elastomers (TPEs) was investigated. The thermal stabilities of the G‐CSP‐TPEs were studied using TGA; Young's modulus of the G‐CSP‐TPEs was studied by means of the spherical indentation test and the tensile test, and the tensile test was also used to characterize the tensile strength of the G‐CSP‐TPEs. The results revealed that the specific functional groups of GPTMS were efficiently grafted onto the CSP and that G‐CSP enhanced the thermal stability of the TPEs. Under 8% strain, Young's moduli of 0–7.5 wt% G‐CSP‐TPEs obtained by the spherical indentation test and tensile test were almost equal, while the modulus of 10–15 wt% G‐CSP‐TPEs measured by the latter test was greater than that of the former test. The tensile strength of G‐CSP‐TPEs increased up to a threshold limit (10 wt% G‐CSP), followed by a significant decrease. Micro‐images of the fractured surfaces obtained by SEM indicated that the addition of G‐CSP gradually filled the microvoids in the matrix and enhanced the tensile strength of the composite. As the G‐CSP mass percentage exceeded a threshold limit (>10 wt%), the particles started to agglomerate, resulting in weak interfacial adhesion and inferior mechanical properties. Hence, an optimal amount of reinforcing agent G‐CSP should be added to attain desirable thermal and mechanical properties. © 2020 Society of Chemical Industry     

有机物对低温超强碱法制备纳米四方多晶氧化锆粉体性能的影响

利用低温超强碱法制备出了纳米四方多晶氧化锆粉体。为改善该粉体分散性较差、氧化钠含量较高的缺点 ,用有机物对粉体进行了表面改性处理 ,采用X射线荧光光谱、X射线衍射、透射电镜等对粉体性能进行了分析。结果表明 ,采用无水乙醇和柠檬酸铵对粉体进行改性处理 ,使得粉体粒度均匀、分布变窄 ,形态近球形 ,其中柠檬酸铵的处理效果尤为显著 ,使粉体平均粒径从 0 .6 9μm减小到 0 .5 4μm ;进一步的高分辨像分析结果表明 ,粉体颗粒多由 2～ 3个大小为 2 0～ 30nm的单晶组成 ,较大的团聚体较少 ,因此有机物对粉体的表面改性处理有利于获得分散性好、粒度均匀的高质量纳米氧化锆粉体。     

超分散剂对二氧化钛粉体分散稳定性的影响

采用超分散剂改性二氧化钛,研究超分散剂浓度、用量、温度等条件对其分散稳定性的影响,找出最佳改性方案。     

Detection of SCC on prestressing steel wire by the simultaneous use of electrochemical noise and acoustic emission measurements

Electrochemical voltage and current noise were measured simultaneously with acoustic emission (AE) measurements during the stress-corrosion cracking (SCC) of prestressing steel wire. Elongation of the specimens was also measured. Constant load tests were performed on specimens made from prestressing steel with a diameter of 3.2 mm: the central wire of a seven-wire strand was used. The specimens were exposed to diluted sodium thiocyanate (a modified version of the test as proposed in EN ISO 15630-3), with and without the addition of an organic corrosion inhibitor. EN was measured between the stressed central cold-drawn wire and the neighbouring wires which acted as reference electrodes for the electrochemical current and voltage measurements. AE was measured by two AE sensors fixed to the specimen.In order to characterize the SCC processes on the prestressing steel wire, the results of all the used techniques were analysed and compared. The effect of the inhibitor on these processes was also studied. A significantly longer time to failure was observed in the experiments with the added inhibitor. The results of the techniques, in combination with SEM and metallographic inspections, confirmed that the inhibitor had a specific influence on SCC. It was concluded that measurements of combined methods are promising for the reliable detection of SCC.     

Resistance of metallic substrates protected by an organic coating containing aluminum powder

The corrosion behavior of an epoxy primer containing aluminum powder (10 vol.%) applied on carbon steel and on galvanized steel was examined by electrochemical impedance spectroscopy (EIS). The data show that this coating is more protective when applied onto carbon steel substrates, and that on galvanized steel thicker coatings allow to achieve similar protection levels as those obtained for carbon steel. These effects are probably due to aluminum pigments providing a cathodic protection of the substrate, and to the resulting products precipitating inside the pores of the polymeric coating. Three stages can be distinguished during exposure of the coated specimens. Upon immersion of the coated samples in the test solution, a pre-saturated stage is observed. After a certain period of immersion, which strongly depends on the thickness of the applied coating, a saturation stage is reached in which an effective protection of the metallic substrate against corrosion is achieved. Finally, at sufficiently long exposure times, swelling through the coating eventually leads to the detachment of the coating.